Answer:

There is nothing in GOST R51274-99.8 to limit the half apex angle of the skirt.

But this is a usual rule, this limitation exists in AD S3/1 4.2 and in CODAP C9.7.1. (French code) to avoid the increase of bending moment due to the horizontal component of the compressive load.

Note well: the message (#35) is a Warning not an Error since there is nothing in GOST.